1. Field of the Invention
The present invention relates to an antenna device suitable for application to mobile terminal equipment such as mobile phones, PHS phones (PHS: Personal Handyphone System) and PDA equipment (PDA: Personal Digital Assistant) having communication functions, and relates to a mobile terminal apparatus equipped with such an antenna device. More particularly, the present invention relates to an antenna device which is constructed so that its corresponding characteristic (antenna characteristic) can be easily adjusted, and a mobile terminal apparatus equipped with such an antenna device.
2. Description of Related Art
Japanese Patent Application Publication (KOKAI) No. 2001-130619 (page 4: FIG. 1) has heretofore disclosed an inverted F antenna which permits fine adjustment of its resonant frequency.
The inverted F antenna includes an antenna section which has a feed terminal connected to a radiating device and first and second frequency switching terminals, and the frequency switching terminals are respectively first and second switches controlled by a control circuit. The control circuit performs switching control of the first switch to connect the first frequency switching terminal to ground directly or via an inductor, thereby enabling switching between resonant frequencies.
In addition, the control circuit performs switching control of the second switch to connect the second frequency switching terminal to ground or open the second frequency switching terminal, thereby enabling switching between further resonant frequencies. The inverted F antenna permits the resonant frequencies to be changed through inductance or the like, so that the inverted F antenna enables fine adjustment of the resonant frequencies and permits an arbitrary frequency to be selected from neighboring frequencies.